1. Field of the Invention
The present invention relates to a method of attaching an additional image to a one-page image obtained by drawing one or more objects including a bitmap object, in a predetermined sequence, and also to a processing system that uses the method.
2. Related Art
During the printing of a document or the like created by application software, a technique is known in the art of attaching an additional image called a watermark to an image of the document that is to be printed (hereinafter called a “main image”). The watermark could be text, such as “Company Secret”, “Copy”, or “Confidential”.
The attachment of a watermark is a function that is generally incorporated within a dedicated driver software for a printing device (such as a printer). When it comes to printing a document created by the application software, a main image with a watermark attached thereto is output for printing by a user specifying an instruction to attach a watermark from a print setting screen of the driver software and also selecting a watermark that is to be attached.
Watermarks could of course be formed of text data, but the watermarks could also be created as image data in a format such as a bitmap. In addition, although such watermarks could be provided by a driver software as default, a user could also create them new.
When a watermark is attached to a main image, the watermark could either be attached in front of the main image (hereinafter called “forward attachment”) or be attached behind the main image (hereinafter called “rearward attachment”). Depending on the driver software, the configuration could be such that the user can select either of these methods, but a default setting of rearward attachment is usually common.
With forward attachment, as shown specifically in FIG. 21(a), the main image is drawn first and finally the watermark is drawn on top of the main image (overwriting), so the watermark has priority in portions at which the main image and the watermark are overlaid, erasing the portions of the main image.
With rearward attachment, as shown specifically in FIG. 21(b), the watermark is drawn first and the main image is drawn over the watermark, so the main image has priority in portions at which the main image and the watermark are overlaid, erasing the portions of the watermark.
A main image created by presentation software, however, generally include of a background object representing a background (an object in bitmap format) and various objects for the presentation, which are drawn overlapping on the background object.
In other words, when a main image of such a configuration is finally rasterized by a printing device, first a background object is drawn and then various other objects are drawn on top of the background object. In general, a background object is often drawn over a comparatively wide range of one page, and a background object could even cover the entire page.
For that reason, if the rearward attachment is employed when outputting such a main image with a watermark attached thereto for printing, it is highly likely that the watermark will hide behind the background object. If the region in which the watermark is drawn is completely comprised within the region in which the background object is drawn, the watermark will be overdrawn by the background object and will be completely erased thereby, as shown in FIG. 21(c).
If the background object in this case is colored, a user seeing the printed result can confirm visually that “the watermark has been erased by the background”, and it is also possible that the user might wish to erase the watermark intentionally with the background.
However, it is also possible to have a background object that is a completely white area or just a frame surrounding white (in the example shown in FIG. 21(c), the background object is completely white except for the frame). Since it would seem to the user that there is nothing drawn in that white area in such a case, the user would be unaware that the white background object has been drawn there in practice and would naturally expect to see the watermark printed in that white portion (which is actually a white background object).
However, in practice the watermark is overwritten by the white background object (the white bitmap object) and is not printed. In other words, from the user's viewpoint, the printed result might cause the user to wonder whether there is a fault in the driver software or the printing device, raising feelings of unease and inconvenience, since there is no watermark drawn in the white area that is supposed to have a watermark drawn therein.
In order to overcome this problem, Japanese Patent-Application Publication No. HEI-11-149355 proposes a technique that is to determine, for a character string object within one page, whether or not it is a character string object that is either not overlaid by another object or not requiring consideration of overlapping, to ensure that each character string object that is overlaid by another object and requiring consideration of overlapping is printed reliably.
This technique ensures that the watermark is printed above another object when the another object overlaps the watermark. However, since this technique does not determine whether the another object is a background or an object that is not a background, the watermark is always drawn at the front.
For that reason, if the above-described technique is used for attaching a watermark to a main image created by presentation software when printing out, the watermark is printed reliably, but main objects other than the background would be hidden by the watermark, which is not in line with the user's intentions of “I want to print a watermark but I also want to print all non-background objects reliably.”
It is also conceivable to use the previously-described forward-attachment for displaying the watermark reliably. However, in this case, the watermark will be displayed unconditionally at the foremost position, giving rise to a similar problem to the above (in that objects other than the background are also covered by the watermark), which is not in line with the user's intentions.